Mars: The Muddy Red Planet?

HiRISE image of a distinctive flow deposit southwest of Cerberus Fossae on Mars -- the feature may have been identified as an ancient mud flow.

NASA/JPL-Caltech/University of Arizona

Gallery

Mind-BlowingBeautyofMars'Dunes:HiRISEPhotos

View Caption+

Mars plays host to a huge number of dune fields -- regions where fine wind-blown material gets deposited to form arguably some of the most beautiful dunes that can be found on any planetary body in the solar system. Using the powerful High-Resolution Imaging Science Experiment (HiRISE) camera on board NASA's Mars Reconnaissance Orbiter, planetary scientists have an orbital view on these features that aid our understanding of aeolian (wind-formed) processes and Martian geology. Here are some of our favorite Mars dunes as seen by HiRISE.
Pictured here are shell-like " barchan dunes " in the ancient Noachis Terra region of Mars.
Special thanks to Ari Espinoza of the HiRISE team at the University of Arizona for helping to compile this list.
PHOTOS: The Weirdest Craters on Mars

NASA/JPL-Caltech/University of Arizona

View Caption+

Dunes of many shapes, sizes and formation processes can be found on the Red Planet. Shown here are elegant " linear dunes " with deposits of larger rocks and possibly ices in their troughs.
READ MORE: Sand Dunes Could Reveal Weather on Alien Worlds

dome dunes " -- elliptical accumulations of fine material with no-slip surfaces. These domes contrast greatly with the often jagged appearance of barchan dunes. Found at the bottom of Proctor Crater, they are darker than the surrounding crater floor as they are composed of dark basaltic sand that was transported by the wind.
READ MORE: Slug-Like Dunes on Mars

NASA/JPL-Caltech/University of Arizona

View Caption+

Looking like a wind-blown silk sheet, this field of "star dunes" overlays a plain of small ripples, another aeolian feature. The ripples move more slowly across the bottom of Proctor Crater, so the large dune field will travel over the smaller ripples. Dunes are continuously evolving and moving with the wind, ensuring that the Martian surface is never static.
READ MORE: Bouncing Sands of Mars Blow in the Wind

Resembling the mouths of a shoal of feeding fish, this is a group of barchan dunes in Mars' North Polar region. Barchan dunes betray the prevailing wind direction. In this case, the prevailing wind is traveling from bottom right to top left; the steep slope of material (plus dune "horns") point to the downwind direction. The HiRISE camera monitors barchans to see if they move between observing opportunities, thereby revealing their speed of motion across the Martian plains.

NASA/JPL-Caltech/University of Arizona

View Caption+

This is the same barchan dune field, zoomed out, a "swarm" of dunes covering the plains.

NASA/JPL-Caltech/University of Arizona

View Caption+

Not all barchan dunes "behave" and form neat "horny" shapes. They can become muddled and overlapping, creating "barchanoid dunes," as shown here.

NASA/JPL-Caltech/University of Arizona

View Caption+

This very fluid-looking collection of barchans is accompanied by a wind-blown ridge in the Hellespontus region of Mars but...

NASA/JPL-Caltech/University of Arizona

View Caption+

...only when zoomed out does the true nature of this fascinating region become clear. The prevailing wind is eroding the mesas (small hills) to the right of the image, carrying fine material downwind (from right to left), creating a startling pattern of barchans and a viscous-looking trail of sandy ridges across the plains.

NASA/JPL-Caltech/University of Arizona

View Caption+

The band Train sang about the "Drops of Jupiter" -- what about the "Drops of Mars"? Sure, they're not made of any kind of fluid, but they do make for incredibly-shaped dunes. These raindrop-shaped dunes are found in Copernicus Crater and are known to be rich in the mineral olivine, a mineral that formed during the wet history of Mars' evolution.
READ MORE: Mars' 'Raindrop' Sand Dunes Swarm

NASA/JPL-Caltech/University of Arizona

View Caption+

These craggy-looking dunes are old barchanoids eroding away through seasonal processes (sublimation of sub-surface ices) and the persistent Martian wind.

NASA/JPL-Caltech/University of Arizona

View Caption+

These linking barchan dunes are at the leading edge of a dune field -- grains of dust have been blown across a plain, deposited and left to accumulate in elongated arrow shapes.

NASA/JPL-Caltech/University of Arizona

View Caption+

Dome-shaped dunes and barchans seem to "reach out" and touch their downwind partners with slumped material.

NASA/JPL-Caltech/University of Arizona

View Caption+

Barchan dunes inside Arkhangelsky Crater in the southern hemisphere of Mars reveal a wind direction from top left to bottom right. Note the tracks of Martian dust devils over the dune slopes.
For more on the HiRISE camera, see the HiRISE website and regularly updated Tumblr page . For more on Mars dune definitions, check out the USGS Mars Dunes site .

Some of Mars' lava fields may actually be massive mud flows, say planetary scientists after taking a detailed look at the distinctive Cerberus Fossae, indicating that the ancient feature may not have been caused by volcanic activity at all.

The Mars rover Curiosity just found out that Martian soil is 2 percent water!

If this is the case, then many other Mars lava flows need to be reexamined, argue Lionel Wilson of the University of Hawai'i, Manoa, and Peter Mouginis-Mark of Lancaster University in new research published in the journal Icarus.

Using models and the latest elevation maps of Ceberus Fossae, the researchers concentrated on the velocity and depth of the flow textures seen as the material cut around boulders and washed up on slopes.

If it was lava, the behavior would be pretty similar to lava on Earth, which often has a broken, platy crust on top that shows how it flowed before cooling and solidifying.

But would mud flows have a platy crust too? The authors propose that the mud, after it erupted from the ground, oozed down the slope in a way unlike any mudflow on Earth. For one thing, the lower atmospheric pressure of Mars would cause the water inside the mud flow to boil. But because Mars' atmosphere is very cold, the mud on top of the flow would be in direct contact with the air and soon freeze to create the platy crust.

"It probably sounds odd that you can boil and freeze water at the same time, but at Mars atmospheric pressure that can and does happen," said Wilson. The viscosity of the mudflow would have been about that of SAE 40 motor oil, he said.

The speed and manner that the lava flowed was important as well. The researchers believe it had very little turbulence within the flow to create the features seen today.

"The key issue is that flows with surface textures like this one that are seen elsewhere on Mars have been assumed to be lava flows," said Wilson. "But if our estimates of the flow speed and depth are correct, then any lava moving with this depth and speed would have a very low viscosity and would be turbulent."

But the surface textures of Cerberus Fossae, and especially the way the textures are preserved when the flow splits and recombines around obstacles, suggest that this flow was very smooth -- something that's called laminar flow. "So how can you get a laminar flow that has a low viscosity?"